1. Field of the Invention
The present invention relates to a thin-film magnetic head with a heater, a head gimbal assembly (HGA) with the thin-film magnetic head and a magnetic disk drive apparatus with the HGA.
2. Description of the Related Art
In a magnetic disk drive apparatus, when writing or reading signals, a thin-film magnetic head hydrodynamically flies with a predetermined spacing on a rotating magnetic disk. While flying on the magnetic disk, the thin-film magnetic head writes signals to the magnetic disk using magnetic fields generated from an inductive write head element, and reads signals by sensing magnetic fields corresponding to the signals from the magnetic disk through an magnetoresistive (MR) effect read head element. On these occasions, a magnetic spacing dMS is defined as the effective magnetic distance between ends of these magnetic head elements and the surface of the magnetic disk.
With the higher recording density due to the increasing data storage capacity and the miniaturization of the magnetic disk drive apparatus in recent years, a track width of the thin-film magnetic head is becoming smaller. The smaller track width causes the writing and reading performance of the magnetic head to be reduced. In order to avoid this problem, latest magnetic disk drive apparatuses have a tendency to reduce the magnetic spacing dMS. The value of the magnetic spacing dMS is actually designed to be reduced down to the order of 10 nm.
However, during writing signals, a Joule heat and a heat caused by eddy-current loss are generated from the inductive write head element. These heats raise a thermal pole tip protrusion (TPTP) phenomenon. In the case of the phenomenon, when the designed value of the magnetic spacing dMS is very small, the protruding MR read head element is at risk of contacting the magnetic disk surface, and a frictional heat generated by the contact may cause the electrical resistance value of the MR read head element to change, raising the problem such as an abnormal signal (thermal asperity).
To avoid this thermal asperity, some methods of providing a heater in the vicinity of the magnetic head elements to positively generate a TPTP phenomenon and controlling the magnetic spacing dMS are proposed (e.g., U.S. Pat. No. 5,991,113, and US Patent Publications Nos. 2003/0174430 A1 and 2003/0099054 A1).
The heater needs to be provided in a position opposite to an air bearing surface (ABS) in relation to the magnetic head elements in order to protrude the magnetic head elements toward the magnetic disk surface by the heat generated from the heater. When the heater is provided in this position, a layer for controlling heat conduction between the heater and the slider substrate can be provided in order to prevent heat dissipation from the heater to the slider substrate. However, in the case with the heat control layer, the heater is at risk of melting due to the increase in the temperature of itself. To avoid the risk, a heatsink layer can be provided in a position opposite to the slider substrate in relation to the heater. A technique in which the heatsink layer suppresses the thermal expansion of the inductive write head element by receiving heat generated from the element is described, for example, in US Patent Publication No. 2004/0017638 A1.
However, when the heatsink layer is provided adjacent to the heater, the problem of the decease in the protrusion efficiency of the magnetic head elements by the heat generated from the heater is often happened.
That is to say, most of the heat that arrives in the heatsink layer from the heater is then dissipated from the heatsink layer surface opposite to the heater, toward the surrounding overcoat layer. Therefore, the heatsink layer causes the heat flow that reaches the neighborhood of the magnetic head elements from the heater to be decreased. Consequently, the heat generated form the heater does not sufficiently reach the neighborhood of the magnetic head elements, so the thermal expansion that protrudes the magnetic head elements is not satisfactorily generated and the protrusion efficiency is decreased.
Due to the decreased protrusion efficiency, more electric power is needed in order to control the magnetic spacing dMS. Therefore, it is difficult to lower the power consumption of the magnetic disk drive apparatus and to miniaturize the apparatus, which is recently tried to be incorporated into a mobile device such as a cellular phone.